Use node-set-status operation to set a specific status for a service node. Use filter-id, filter-ip or filter-hostname to specify the target service node.

Request 

<packet>
  <extension>
    <call>
      <plesk-multi-server>
        <node-set-status>
          <status>active</status>
          <filter-id>1</filter-id>
        </node-set-status>
      </plesk-multi-server>
    </call>
  </extension>
</packet>

Response 

<packet>
  <extension>
    <call>
      <result>
        <status>ok</status>
        <plesk-multi-server>
          <node-set-status/>
        </plesk-multi-server>
      </result>
    </call>
  </extension>
</packet>